Control system for press brakes and the like

ABSTRACT

A control system for a press brake having a frame, a bed, a ram, and a hydraulic system for reciprocating the ram toward and away from the bed. Top and bottom limit switches, actuated by the ram, are provided for establishing the maximum ascent and descent of the ram, and a speed control limit switch, disposed between the top and bottom limit switches, defined a work stroke wherein the ram in descending is slowed as it comes into contact with a work piece for greater accuracy and operator safety. To prevent set-up adjustments to the bottom limit switch from affecting the length of the work stroke, a novel mechanical coupling arrangement is provided whereby the position of the speed control switch is automatically shifted to compensate for changes in the position of the switch. Means are also provided for coupling the top limit switch to the speed control limit switch to achieve a constant overall ram operating cycle.

United States Patent 1191 Hryc Oct. 15, 1974 [54] CONTROLVSYSTEM FOR PRESS BRAKES 3,552,182 1/1971 Handler 72/453 AND THE LIKE l/l972 Anderson 72/22 75 l t h F. H Ch' lll. l i or J rye Primary Examiner-C. W. Lanham [73] Ass1gnee: Dreis & Krump Manufacturing Ass/slam E R, Dylan Company, Chicago, 111.

[22] Filed: D26. 18, 1972 57 ABSTRACT [21] Appl' 315,810 A control system for a press brake having a frame. a bed, a ram, and a hydraulic system for reciprocating 52 U.S. c1 72/441, 72/25, 72/26, the toward and away from the P and I 72 443 100 25 torn limit switches, actuated by the ram, are provided [51] Int. Cl B2lj 7/46 for establishing the maximum ascent and descent of [58] Field of Search 72/21, 26, 441, 443, 389, the ram, and a Speed Control limit Switch, disposed 72/453 tweenthe topand bottom limit switches, defined a work stroke wherein the ram in descending is slowed [5 References Cited as it comes into contact with a work piece for greater accuracy and Operator Safety. TO prevnt Set-up adjustments to the bottom limit switch from affecting the g f length of the work stroke, a novel mechanical cou- 3046874' 7/l962 3 2 a [00/256 pling arrangement is provided whereby the position of 3062l32 [1962 Deb 100/256 the speed control switch is automatically shifted to 3:142:206 7/1964 Hague et al 72 2 compensate for changes in the position of the switch. 3,165,140 1/1965- 'Hazelton et a1... 72/2 Means are also provided for coupling the top limit 3,191,412 6/1965 Duvall 72/26 switch to the speed control limit switch to achieve 21 3,429,156 2/1969 Eriksson' 72/26 constant overall ramoperating cycle, 3,451,236 6/1969 Fowler et al.. 72/25 3,469,435 9/1969 Trautman 72/453 10 Claims, 7 Drawing Figures I IO 1 i l 1' 12 14 l l l v i 1 v s i l /32 5 -24 I 16* e1] 9 [El 1 v 17 h 1 /\2O 18 5 11 I PAIENIEB w 1 51am FIG. 2

SIEEI 1 or 4 Emma; um 51914 SIKHZOF 4 FATE-M83 I 51874 3.841 140 mm a or A ""'It Regulating WW6 FIG. 7

Left Cyl.

Right 14 15 Cyl- Advance Sol.

215OPSI V rel ZOO PS1 V rel Left Cyl. Up Sol.

Left Cyl. Down Soi.

Right Cyl. Down Sol.

Up Sol.

2 250 PSI V rel Hydraulic Pump Motor CONTROL SYSTEM FOR PRESS BRAKES AND -THELIKE. y

BACKGROUND OF HE INVENTION with coacting dies and the work piece to be formed or sheared is placed between the dies. The hydraulic-ram then bringsthe dies into engagement. with the work piece with sufficient pressure to achieve the desired forming or shearing action.

Often, and particularly where the length of the overall operating stroke of the hydraulic ram is large relative to the portion of the stroke where pressure is actually applied to the work piece, it is desirable'that the ram advance initially at a'relatively fast advance speed I until the die-attached to the ram nears contact with the work piece, then slow; to a lower pressing speed as the die actually engages the work piece and performs the desired forming or shearing operation. This results in a substantial savings in operator and machine time, with out sacrificing the accuracy and safety achieved by the slow pressing speed.

To achieve-this desired two-speed reciprocative, operation of the hydraulic ram, an electrical control system is normally provided on the pressbrake for sensing the position of the ram relative to the work piece and bed and generating appropriate control signals for application to solenoid-operated valves in the hydraulic system which powers the ram cylinders. Typically, such electrical control systems sense ram position by means ofa ram mounted actuator arm and three adjustable limit switches; a top'limit switch for setting the maximum upward-travel of the ram, a speed control limit switch for switching the speed of the ram from the relatively high advance speed to the lower pressing speed as the die mounted on the ram comes into contact with the work piece, and a bottom limit switch for limiting the maximum downward travel ofthe ram to a point just above the bed of the press brake.

One complication of the aforedescribed switch arrangement is that the length of the work stroke, i.e., that portion of the ram operating cycle wherein the dies are engaged with the workpiece, varies as the position or set-up of the bottom stop is adjusted, as may be necessitated by changes in the thickness-of thework piece or by occasional. changes in the pressing operation. This change in the work stroke is often undesirable, since a new work piece will often require the same work stroke as a previous work piece, notwithstanding slight differences in thickness and composition which can be compensated for by a change in set-up. While changes in the set-up of the bottom stop are usually made from the front of the machine, typically by way of a crank which operates a lead screw to vertically po-- sition the bottom limit switch, changes in the positions of the other limit switches are not as easily made and are, at best, a time consuming matter. for both the machine and operator.

Accordingly, it is a general object of the present invention to provide a new and improved control system for a press brake or the like.

It is amore specific object of the present invention to provide a control system for a hydraulic press brake which provides a constant work stroke notwithstanding changes in the set-up of the bottom stop of the hydraulic ram.

lt is a still more specific object of the present invention to provide a new .andimproved control system for a press brake or the like wherein adjustments in the position of the bottom limit switch can be conveniently 'made without changing the length of the work stroke.

It is a still more specific object of the present invention to provide acontrol system for a press brake or the extent wherein a work stroke of predetermined length can be set independently of other operating stroke ad operating stroke of the ram.

SUMMARY OF THE INVENTION Accordingly, the invention is directed to a control system for a press brake of the type having aframe, a bed, a ram, and drive means on the frame for reciprocating the ram along a defined operating path toward and away from the bed. The control system comprises means comprising'a first ram position sensing device positioned along the operating path for limiting the maximum upward excursion of the ram, and means comprising a second ram position sensing device positioned along the operating path for limiting the maximum downward excursion of the ram, the position of the second ram position sensing device being adjustable to effect changes in the set-up of the press brake. Also included are means comprising a third ram position sensing device positioned along the operating path between the first sensing device and the second sensing device for establishing a work stroke for the ram wherein the ram is advanced toward the bed at a reduced rate beyond a predetermined intermediate location along the path, and means for automatically positioning'the third ram position sensing device are included to maintain the length of the work stroke substantially constant notwithstanding changes in the position of the-second ram position sensing device.

BRIEF DESCRlPT ION OF THE DRAWINGS The features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The invention, together with the further objects and advantages thereof, may best be understood by reference to the following description taken in connection withthe accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:

F IG. 1 isa perspective view of a press brake incorporating a control system constructed in accordance with the invention.

FIG. 2 is a side elevational view of thepress brake of FIG. 1 showing a portion of the control system therefore.

FIG. 3 is an enlarged perspective view of a portion of the control system for the pressbrake of FIG. 1.

FIG. 4 is a top view of the portion of the control system shown in FIG. 3 taken along lines 4-4 of FIG. 3.

F 16.5 is an exploded perspective view of certain elements of the portion of the control system shown in FIG. 3.

FIG. 6 is a simplified schematic diagram of the electrical portion of the control system of the press brake of FIG. 1. g

FIG. 7 is a simplified diagram of the hydraulic portion of the control system for the press brake of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, the control system of the present invention is seen to be incorporated in a press brake 10 which, with the exception of the control system, may be conventional in design and construction. The press brake consists of a pair of heavy spaced-apart upstanding side plates 11 and 12 which are joined at their bottom ends by a bed plate 13. A pair of hydraulic cylinders 14 and 15 are mounted at the top ends of side plates 11 and 12, respectively. The pistons of these cylinders are connected to a movable ram member 16 which is constrained by the pistons to reciprocate along a predetermined vertical path extending from the cylinders to the top surface of bed plate 13. An upper die 17is' secured to the bottom edge of ram 16 and a lower die 18 is secured to the top of bed 13 to exert force on a work piece 19 situated between the two dies. While the dies may be of various shapes and sizes, they normally are structured to coact when brought into engagement under pressure to accomplish a forming or shearing operation on an intervening work piece. The two dies are readily changeable by the operator to accommodate specific job functions. 1

Referring now to FIG. 2, ram 16 has an actuator arm 20 attached to it which extends to the rear of the press brake parallel to the outside surface of side plate 12. This actuator arm is utilized to actuate three limit switches associated with the control system for the ram; namely, a top limit switch 21, a speed control limit switch 22, anda bottom limit switch 23. Each of these limit switches is connected by an individual cable to an electrical junction box 24 which houses the major electrical components of the control system. A control panel 25 mounted on the top cover of junction box 24 provides a convenient location for required operatoraccessablecontrols.

To enable the maximum downward extent of the ram opera-ting cycle to be accurately set up, the bottom limit switch 23 is mounted on a vertically adjustable carriage'26. A verticallead screw 27, driven from the front of the press brakemachine by a pair of beveled gears 28, a horizontal shaft 29 extending through bed plate 13, and a crank handle 30, engages carriage 26 and moves it up and down as desired by the operator. A digital turns counter 31 located at the front of the machine adjacent handle 30 androtatably coupled to shaft 29 allows set-ups to be accurately reproduced.

A hydraulic pressure gauge 32 is provided for monitoring the pressing effort of the machine. This gauge contains electrical contacts which can be set by the operator to close and interrupt operation of the press brake when a predetermined maximum pressure is exceeded to prevent damage to the dies'from excessive pressing effort.

Referring now to FIGS. 3and 4, limit switches 21 and 22 are mounted on side plate 12 by means of an elongated L-shaped bracket 33 which is fastened to the side plate by means of an underlying elongated spacer block 34 and appropriate fastening means such as machine bolts 35. .Top limit'switch 21 is mounted on a carriage block 36, which in turn is slidably mounted on bracket 33 by means of a thumbscrew 37. The threaded shank portion of thumbscrew 37 extends through a slot 38 on bracket 33 and engages a complimentarily threaded hole on block 35. By tightening thumbscrew 37 mounting block 36 is drawn into tight frictional engagement with bracket 33 and switch 21 is held in a fixed position.

It will be recalled that bottom limit switch 23 is mounted on a carriage assembly 26, and that this assembly can be positioned vertically by means of lead screw 27. To this end the top end of lead screw 27 is threaded into a tubular vertical support member 41 which is slidably mounted to side plate 12 by means of a pair of brackets 42 and 43. The inside surface of member 41 is at least partially threaded, so that as leadscrew 27 is rotated the support member is driven upwards or downwards, depending on the direction of rotation. Bottom limit switch 23 is mounted on a carriage block 44 which is attached to support member 41 by means of a compression clamp 45. Block 44 and clamp. 45 together form the carriage assembly 26, the latter assembly moving vertically with support member 41.

Referring to FIG. 5, an appropriately dimensioned actuator shoe 46 is mounted to the inside surface of the arm by machine screws 47 or other appropriate fastening means to enable actuator arm 20 to actuate limit switches 21 and '22. Actuator shoe 46 extends sufficiently far towards side plate 12 to depress the two limit switches as arm 20 passes over. Actuator arm 20 also carries at its enda pivotally mounted actuator lever 48 for actuating bottom limit switch 23 as the ram reaches the bottom extent of its travel. This lever is spring biased towards switch 23 by a compression spring 49, but is limited in its clockwise rotation by a cylindrical stop member 50 extending from arm 20. The advantage of this lever arrangement is that the actuator lever 48 is free to pivot counter-clockwise should the ram for any reason fail to stop when actuator arm 20 brings the lever into engagement with limit switch 23, thus preventing damage' to the limitswitch and the actuator arm in that circumstance.

The 'coaction between actuator arm 20 and limit switches 21-23 can best be seen by reference to FIG. 5. Initially, when the ram is at the uppermost extreme of its travel, the actuator shoe 46 depending from arm 20 depresses the roller-ended arm of top limit switch 21. As the ram begins its operating cycle, actuator arm 20 releases limit switch 21'and moves downwardly with the ram at its normal or advancespeed until. actuator shoe 46 depresses the roller-ended arm of speed control limit switch 22. This immediately slows the ram toa slower pressing speed, and the ram continues at this speed until actuator lever 48 contacts the plungerof bottom limit switch 23, at which point the ram is,

stopped. To insure that theram will continue to operate at a slow pressing speed during the working or pressing portion of its cycle the length of actuator shoe 46 is made sufficiently long to extend the entire distance from speed control limit switch 22 to bottom limit switch 23. However, it will be appreciated that this same result can be obtained by means of a conventional electrical latching circuit, the slow down function being then activated by momentary depression of limit switch 22 and being deactivated upon the ram being stopped by bottom limit switch 23.

Thus, the length of the work stroke, i.e., the slowspeed pressing portion of the ram operating cycle, is determined by the relative spacing between limit switch 22 and limit switch 23, which spacing can be initially set by sliding speed control switch 22 into position and tightening thumbscrew 40. However, it will be appreciated that should the position of bottom limit switch 23 be changed for any reason, as by rotation of leadscrew 27 to effect a change in set-up, the length of the work stroke. will change. As mentioned previously, this is often undesirable because it often necessitates readjustment of limit switch 22 to retain the original work stroke, whicn is often a time consuming non-productive effort.

Therefore, and in accordance with the invention, a novel mechanical coupling arrangement is provided between the speed control limit switch 22 and the bottom limit switch 23. Specifically, and with reference to FIG. 3, a fixed spacing is maintained between bottom limit switch 23 and speed control limit switch 22 by means comprising a tie rod 51 and a tie bar 52 which extend between carriage 26 and carriage block 39. Tie rod 51 is secured to a mounting block 53, which in turn is secured to carriage block 44 by a plurality of machine screws 54 or other appropriate fastening means. Tie bar 52 is secured to carriage block 39 by a plurality of machine screws 55 or other appropriate fastening means, and extends downwardly across the end of tie rod 51. Tie rod 51 is'slidably joined with tie bar 52 by means of a thumbscrew 56, which has a threaded shank portion which extends through a slot 57 in tie bar 52 to engage a threaded hole in the end of tie rod 51. When thumbscrew 56 is tightened, tie bar 52 is held in tight frictional engagement with tie rod 51 and the spacing between the limit switches, and hence the length of the pressing cycle, is held constant. Then, to enable limit switch 22 to move vertically with bottom limit switch 23 it is only necessary to loosen thumbscrew 40 so that carriage block 39 is free to slide along bracket 33. Of

course, speed control switch 22 can be independently adjusted if desired, without the benefits of a constant work stroke, by retightening thumbscrew 40 and loosening thumbscrew 56, which willallow carriage block 44 to move independently of carriage block, 39.

In certain instances it may be desirable to maintain the length of the overall operating stroke of theram constant notwithstanding changes in the set-up of bottom limit switch 23. To this end, anadditional means comprising an elongated slotted tie bar 58 is provided for fixing the spacing between limit switches 21 and 22. Tie bar 58',is fastened tothe side-of carriage block 36 by machine screws 59 or other, appropriate fastening means and extends downwardly from block 36 parallel to bracket'33 and along the side of carriage block 39. A thumbscrew 60 has a threaded shank portion which extends through a slot 61 in tie-bar 58 to engage a complimentarily threaded hole in carriage block 39. By

tightening thumbscrew carriage block 39, and hence speed control switch 22, canbe brought into tight frictional engagement with tie bar 58. It will be appreciated that this would have the effect of fixing the distance between switches 21 and 22, and that by then loosening thumbscrews 37 top limit switch 21 could be made to slide along bracket 33 with either switch 22, or with both switches 22 and 23. In the latter instance the length of the overall stroke of the ram would remain constant, notwithstanding changes in the set-up of bottom limit switch 23. Of course, should it be desi'rable to adjust limit switch 21 independently, it is only necessary to loosen thumbscrew 60 and retighten thumbscrew 37. 1

Having seen how the individual limit switches of the control system are actuated by movement of the ram, we will now briefly examine the electrical and hydraulic circuitry associated with these switches in controlling the ram. Referring to the simplified electrical diagram of FIG. 6, the press brake includes'a hydraulic motor operable from a three-phase AC line. The three legs of the AC line are connected to the motor by way of individual fuses 71, the normally open contacts of a motor control relay 72, and the sensing elements of individual circuit breakers 73. A'step-down transformer 74 is connected across two legs of the AC line to provide a low-voltage current source for the control circuits. One terminal of the secondary winding of transformer 74 is connected to one terminal of one pole of a three-pole three-position OFF-INCl-I-AUTO mode switch 75. The other terminal of this pole of switch 75 is connected to one terminal of a normally closed MOTOR STOP push-button switch 76, and the other terminal of this switch is connected to one terminal of a normally open MOTOR START push-button switch 77, whichis shunted. by a set of normally open contacts of relay 72. The other terminal of switch 77 is connected by way of the normally closed contacts of, the three overload circuit breakers 73 to the coil of relay 72. Provided mode switch 75 is in either its INCH or AUTO positions, when MOTOR. START switch 77 is depressed relay 72 is energized and remains so by viture of closure of the shunt contacts around switch 76. This energizes hydraulic motor 70, which continues to run until MOTOR STOP switch 76 is depressed or mode control switch 75 is positioned to OFF.

When mode switch 75 is closed, current is also applied through the normally open contacts 78 of a relay 79, which is energized when the ram is not tilted, to one terminal of one section of top limit switch 21,"which comprises atwo section normally closed switch. When limit switch 21 is closed, which is the case whenever the ram is not in its full up position, current is applied to one terminal of a normally open RAM UP push-button switch 80 and-tov one terminal of each of second and third sets of normally open contacts of mode switch 75.

Switch 80 and contacts 81 are also connected through normally open contacts 85 of relay 84 and the normally closed contacts of a LEFT CYLINDER TILT RESET push button switch 86 to a valve control solenoid 87, which'admits hydraulic fluid to raise the left ram cylinder. Switch 80 and contacts 81 are further connected through a second set of normally open contacts 88 of relay 84 and the normally closed contacts of a RIGHT CYLINDER TILT RESET pushbutton switch 89 to a valve control solenoid 90, which admits hydraulic fluid to raise the right ram cylinder. The first set of contacts of switch 75 is also connected to the arm of a double-throw left tilt limit switch 91. The normally open contact of this switch, which closes when the left side of the ram lags, is connected to a LEFT TILT indicator lamp 92 and through the normally open contacts of switch 86 to solenoid 87. The normally closed contact of limit switch 91 is connected to the arm of a double-throw right tilt limitswitch .93. The normally open contact 'ofswitch 93, which closes when the right side of the ram lags, is connected to a RIGHT TILT indicator lamp 94 and through the normally open contacts of switch 89 to solenoid 90. The normally closed contact of limit switch 93 is connected to the coil of ram tilt relay 79, causing this relay to be energized whenever mode control switch 75 is in either INCHor AUTO and the ram is not tilted to the point where either one of limit switches 91 and 93 is actuated.

The normally open contacts 82 of relay 83 are connected to the coil of that relay. The normally open contacts 78 of relay 79 are also connected through a normally open tonnage limit switch 94 and a second set of normally opencontacts of top limit switch 21 to the coil of relay 83. The normally open contacts 78 of relay 79 are also connected to the arm of a bottom limit switch 95, the normally open' contact of which is connected to the arm of the second set of contacts of switch 21, and the normally closed contact of which is connected through a pair of series-connectednormally open RAM DOWN push-button switches 96 and 97, the normally closed contacts 98 or a relay 84,and the normally closed contacts 99 of relay 83 to the coil of a relay 100, which closes'to move the ram downward.

The normally open contacts 78 of relay 79 are also connected through a set of normally open contacts 101 of relay 100 to the parallel combination of a valve'con of a common return bus 106 to the remaining terminal of the secondary winding of step-down transformer 74.

In operation, when mode control switch 75 is positioned in INCH and'the hydraulic motor 70 is energized as previously described, current is applied through tilt limit switches 91 and 93 to relay 79. This closes contacts 78, allowing current to flow through bottom limit switch 95 to the series-connected RAM DOWN push-button switches 96 and 97. When both'of these switches are simultaneously depressed current is applied to the coil of relay 100, closing contacts 101 and energizing the left cylinder down valve control solenoid 102 and the right cylinder down valve control solenoid 103. This causes the ram to descend at its normal advance speed until the ram speed control limit'switch 105 is actuated, at which time the speed control solenoid 104 is energized and the ram slows to pressing speed. The ram continues to descend at pressing speed until it actuates bottom limit switch 95, which removes current from cylinder down relay 100 and applies current through the second section of top limit switch 21 to the coil of relay 83, energizing that relay and closing contacts 81 and 82.

When mode switch 75 is set for INCH operation, to

3 return the ram to its full-up position it is necessary to depress RAM UP switch 80, which applies current through the now closed first section of top limit switch 21 to the coil of cylinder up relay 84. Upon energization of this relay, the normally open contacts and 88 are closed and the cylinder up valve control solenoids 87 and are energized. This causes the ram to move upward as long as UP switch 80 is depressed. When the ram reaches the top extreme of its travel, top limit switch 21 opens to interrupt current to relay 84, thereby interrupting current to solenoids 87 and 90 and stopping the ram.

When mode switch 75 is set for AUTO operation the cylinder up relay 84 is automatically'energized (when relay '83 is energized) by way of top limit switch 21, which it will be recalled is closed when the ram is not at the top of its cycle, and relay contacts 81. Contacts 82 also close to form a holding circuit for relay 83, and hence relay 84, by applying current to the coil of relay 83 through top limit switch 21 and the third set of contacts of mode switch 75. While relay 84 is energized the ram moves upward until top limit switch 21 is energized, at which time the top limit switch opens and relays 83 and 84 become de-energized. To repeat the ram cycle, it is only necessary to depress RAM DOWN switches 96 and 97. Should the ram become excessively tilted at any point in its operating cycle, the corresponding one of tilt limit switches 91 and 93 would be actuated. This would de-energize tilt limit relay 79 to open contacts 78 and thereby stop the ram. The associatedone of indicator lamps 92 and 94 would also be illuminated by the actuated tilt limit switch to signal to the operator the reason for the interruption. To correct the tilt condition, it would be necessary to depress the corresponding one of TILT RESET push-button switches 86 and 89 to apply current by way of the actuated tilt limit switch to the associated one of valve control cylinder up solenoids 87 and 89 until the tilt condi-- tion is corrected, as evidenced by the indicator lampbeing extinguished as the tilt limit switch is released, which re-energizes relay 79 and enables the ram to proceed.

Having considered the electrical portion of the control system, it remains to consider the hydraulics which are provided to energize the ram cylinders in response to the aforementioned electrical system control functions. Basically, and with reference to the simplified diagram of FIG. 7, the hydraulic system comprises a ,hydraulic pump which is powered by motor 70. This hydraulic pump, which may be a conventional splitflow type pump having provision for balancing flow through two lines, removes hydraulic fluid from a sump or reservoir 111 and supplies it under high pressure to the various valves and hydraulic actuators of the system.

One output'of pump 110 is connected to the-first input of a first ram control valve 112, and the other output of pump 110 is connected to the first input of a second ram control valve 113; Ram control valves 112 and 113 are each three-position valves, having first and second inlets (shown on the bottom of the valve symbols in H0. 7) and first and second outlets (shown on the top of the valve symbols in FIG.'7). Each of the outputs of pump 110 is also connected by a respective one of check valves 114 and 115 to a high pressure relief valve 116, which opens the lines to reservoir 111 should the pump output pressure exceed a' predeter- 15, and the s'econd'outlet is connected to the top port mined maximum value. In practice additional control valves may be provided at the outputs of the pump to shut off the system should the pressure fail forany reason in one of the lines. Also,-a low pressure actuator system would normally be employed for manipulating the valvesjin response to valve closings accomplished in the low pressure system by the electrical control systern. This system which may be entirely conventional in design and construction, is not shown in this diagram for the sake of clarity. Instead, the valve control sole noids of the; electrical control system are shown as directly associated with the high pressure valves, it being understood that the actual manipulation may be accomplished by a low pressure system.

The hydraulic system includes means in the form of a tilt regulating servo valve 117 for insuring that each 1 end of the ram travels at an equal rate. A control tape or wire 118 extending lengthwise to the ram, being wrapped about a guide pulley atone end and extending downwardly to a fixed anchor point on the machine frame, and being wrapped about a guide pulley at the other end and extending upwardly to the spool of valve 117, provides an input to the servo valveindicative of the degree and direction of tilt of the ram. The resulting change in the position of the spool of the valve 117 causes the valve to effect a compensating change-in the relative rate of feed of hydraulic fluid to the'two ram cylinders. 1n the present system this is accomplished by.

means of connections extending from the two inputs of servo valve 117 to the two output lines from hydraulic pump 110, the valve selectively connecting one or the other or both of these inputs to a common output which discharges into reservoir 111.

Ram control valves 112 and 113 each have three opcrating positions. In the first position, i.e., that shown on the left side of the valve and attainable by energizing solenoids 87 and 90, the two inlets and twooutlets of each valve are cross-connectedi'ln the'ce'nter position of the two valves; i.e.,that attainable when no solenoids are energized, the two inlets areconnected to the first outlet and the other outlet' is blocked.ln the third posiof the ram cylinder 14. The first outlets of valves 112 and 1 13 are also connected by respective ones of check valves 121 and 12 2 to a pressure relief valve 123, which opens the lines to fluid reservoir 111 under a relatively low predetermined maximum pressure, and by respective ones of check valvesl24 and 125 to the first and second inlets (shown on the top of the valve symbols-in FIG. 7) of a two position ram speed control valve 126. This valve provides a direct connection between respective ones of its inlets and outlets when the associated cylinder speed control solenoid 104 is energized, and blocks all inlets and outlets when the solenoid is de-energized. The second outlets of ram control valves 112 and 113 are also connected by respective ones of check valves 127 and 128 to a pressure relief valve 129, which opens the lines to reservoir 111 when the pressure in the lines exceeds arelatively high predet'e'rmined level. The second outlets of valves 112 and 113 are also connected to respective ones of the outlets of valve 126, and to the hydraulic pressure gauge 32, which it will be recalled indicates the pressing effort exerted by the ram. The first inlets of valves 112 and 113 are connected to the sump reservoir 111.

In operation, motor is energized and hydraulic pump pressurizes the lines leadingto the ram control valves 112 and 113. Pressure relief valve 116 as provided at this point to relieve excess hydraulic pressure, and check valves 114 and 115 are provided to preclude the possibility of reverse flow from reservoir 111 into the system. Assuming the ram to be stopped and all of'the solenoids to be de-energized, thehydraulic pressure applied to the second inlets of control valves 112 and 113 is vented through the first inlets of these valves to reservoir 111. At the same time check valves 119 and'120 prevent the ram from descending by blocking outflow from the bottom ports'of the two ram cylinders, the other outflowpath being blocked by pressure relief valve 123, which is set to require a pressure greater than that provided by the weight of the ram. Typically, this valve may be set to open at 200 psi.

Assumingnow that the ram is to be cycled downwardly and the right cylinder down solenoid 103 and the left cylinder down solenoid 102 have been energized by the electrical circuitry of the system, control valves 112 and 113 establish straightthrough connections and-pressure is applied to the top ports of the left and right ram cylinders 15'and 16. The bottom ports of cylinders 14 and. 15 are vented to fluid reservior 111 by way of check valve 121 and 122, respectively, and the low pressure relief valve 123. It will be recalled that the ram initially moves at a fast or advance speed, and then slows to a slow or work speedasit contacts the work peice. The electrical control system controls this change by. energizing solenoid 104 during the full speed or advance portion of the cycle, and by de-energizing the solenoid during the pressing portion of the cycle.

When solenoid 104 is energized, straight-through connections are established between its inlets and outlets, allowing fluid to freely flow through check valves 124 and 125 from the respective bottom ports to the top ports of cylinders 14 and '15 as the ram descends. As

the ram comes into contact with the work piece, the normally closed speed control limit switch 105 is actuated and solenoid 104 is de-energized. This causes.

valve 126 to close, terminating the flow between the upper and lower ports of the cylinder and thus slowing the descent of the, ram.

When the ram reaches'the full extent of its downward travel, solenoids 103 and 102 are de-energized and valves 112 and 113 return to their Center position. Since no fluid can now flow to the ram cylinders, the pressing effort of the ram is terminated. Assuming the electrical control system to now be conditioned to move the ram upwardly, the left cylinder up solenoid 87 and the right cylinder up solenoid 90 are energized. This cross-couples the inlets and outlets of ram control valves 113 and 114 so that the fluid under pressure is applied through check valves 119 and 120 to the bottom ports of left and right ram cylinders, 14 and 15, respectively. Pressure relief valve 123 is normally closed during this portionof the cycle since the pressure required to raise the ram is less than that required'to open the valve. While the ram is being raised, the top ports of left and'right ram cylinders 14 and 15 are coupled by valves 113 and 112, respectively, to reservoir 111 to drain fluid from the top of the ram piston as the rain rises. When the ramfinally'reaches its top orlhome' position, ram control valves 112 and 113 are again returned to their neutral position and application of pressure from hydraulic pump 110 to the system is terminated.

Thus, by virtue of the electrical and hydraulic control systems, as the ram proceeds downwardly from its top position toward the work piece, it proceeds at a fast or advance rate, typically in the order of 62 inches per minute, until speed control limit switch 105 is actuated by actuator shoe 46 on the rammounted actuator arm 20. The ram then slows to a pressing speed, typically in the order of 27 inches per minute for the remainder of its descent until the bottom limit switch 23 is eventually actuated by lever 48, at which time the ram stops. It will again. be appreciated that the length of this work position of the ram-operating cycle is dependent on the spacing between limit switches 22 and 23, and that this spacing can be made uniform in accordance with the present invention by maintaining a fixed spacing between limit switches 22 and .23, notwithstanding changes in the set-up of limit switch 23.

Thus, a novel control system has been described for a press brake which provides a work stroke of uniform length notwithstanding changes in the set-up or position of the bottom limit switch. This provides a significant savings in time, and allows changes-in set-up to be rapidly accomplished by an operator from the front of the machine without the necessity of adjusting the setup of the individual limit switches. In this respect provision is made in the illustrated embodiment for rapid adjustment of one, two or three of the limit switches by means of a front operated depth control, or for-alternately adjusting the switches individually should the job so require. f 1 Y While a particular embodiment of the invention has been shown and described, it-will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall with the true spirit and scope of the invention.

I claim:

1. In a press brake of the type having a frame, a bed, a ram, and drive means on said frame for reciprocating said ram along a defined operating path toward and away from said bed, a controlsystem comprising:

means comprising a first ram position sensing device positioned along said operating path for limiting the maximum upward travel of said ram; means comprising a second ram position sensing device positioned along said operating path for limiting the maximum downward travel of said ram, the position of said second ram position sensing device being operator-adjustable to effect changes in the downward travel limit of said ram to accommodate variations inthe thickness of work pieces on said bed;

means comprising a third ramposition sensing device positioned along said path for establishing a work stroke for said ram wherein said ram is advanced toward said bed at a reduced rate beyond a predetermined intermediate location along said path; and

means for automatically repositioning said third ram position sensing device as the position of said second ram position sensing device is changed to maintain the lengthof said work stroke substantially constant notwithstanding said operator- ,initiated changes in the downward travel limit of said ram.

2. A control system as defined in claim 1 wherein said means for automatically positioning said third ram position sensing device comprise a mechanical coupling between said second and third ram position sensing devices.

-3. A control system as defined in claim 2 wherein said mechanical coupling comprises a spacer for maintaining a fixed spacing between said second and third ram position sensing devices.

4. A control system as defined in claim 3 wherein said second andthird ram position sensing devices are slidably mounted on said frame parallel to said ram operating path.

5. A control system as-defined in claim 4 wherein said second and third ram position sensing devices comprise electrical limit switches.

6. A control system as defined in claim 1 wherein said third ram positionsensing device is positioned between said first and second ram position sensing devices.

7. A control system as defined in claim 4 wherein said first ram position sensing device is also slidably disposed along said path, and wherein means are provided for mechanically coupling said first ram position sensing device to said second ram position sensing device to maintain the overall excursion of said ram between said upper and lower travel limits constantnotwithstanding changes in the position of said second ram position sensing device.

8. A control system as defined in claim 5 which fur ther comprises an actuator arm carried on said ram and arranged to move reciprocatively along said definedoperating path therewith, said actuator arm being adapted to actuate said third and second limit switches as said ram descends from said upper travel limit position along said defined operating path.

9. A control system as defined in claim 4 which further comprises an operator-actuable lead screw for changing the position of said second ram position sensing device.

10. in a press brake of thetype having a frame, a bed, a ram, and drive means on said frame for reciprocating said ram along a defined operating path toward and away from said bed, a control system comprising:

means comprising a first limit switch positioned along said operating path for limiting the maximum upward travel of said ram;

means comprising a second limit switch slidably mounted on said frame along said operating path for limiting the maximum downward travel of said ram, the position of said second limit switch being operator-adjustable to effect changes in the downward travel limit of said ram to accommodate variations in the thickness of work pieces on said bed;

means comprising a third limit switch slidable mounted on said frame along said operating path ram.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,841,140 Dated October 15, 1974 Inventor(s) John HrYC It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 2, line 18, "extent" should be ---like---;

Col. 2, line 23, "extend" should be --extent-;

Col. 6, lines 42 and 43, "viture" should be --virtue--;

Col. 10, line 46, "straightthrough" should be -straight through-;

Col. 13, line 13, "slidable" should be -slidably-;

Col. 14, lines 11 and 12, "operatorinitiated" should be operator initiated.

Signed and sealed this 29th day of April 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks FORM uscoMM-oc scan-Pea v lLS. GQVIINHEN'I' PRINTING OFFICE 2 I." 8"-:, 

1. In a press brake of the type having a frame, a bed, a ram, and drive means on said frame for reciprocating said ram along a defined operating path toward and away from said bed, a control system comprising: means comprising a first ram position sensing device positioned along said operating path for limiting the maximum upward travel of said ram; means comprising a second ram position sensing device positioned along said operating path for limiting the maximum downward travel of said ram, the position of said second ram position sensing device being operator-adjustable to effect changes in the downward travel limit of said ram to accommodate variations in the thickness of work pieces on said bed; means comprising a third ram position sensing device positioned along said path for establishing a work stroke for said ram wherein said ram is advanced toward said bed at a reduced rate beyond a predetermined intermediate location along said path; and means for automatically repositioning said third ram position sensing device as the position of said second ram position sensing device is changed to maintain the length of said work stroke substantially constant notwithstanding said operatorinitiated changes in the downward travel limit of said ram.
 2. A control system as defined in claim 1 wherein said means for automatically positioning said third ram position sensing device comprise a mechanical coupling between said second and third ram position sensing devices.
 3. A control system as defined in claim 2 wherein said mechanical coupling comprises a spacer for maintaining a fixed spacing between said second and third ram position sensing devices.
 4. A control system as defined in claim 3 wherein said second and third ram position sensing devices are slidably mounted on said frame parallel to said ram operating path.
 5. A control system as defined in claim 4 wherein said second and third ram position sensing devices comprise electrical limit switches.
 6. A control system as defined in claim 1 wherein said third ram position sensing device is positioned between said first and second ram position sensing devices.
 7. A control system as defined in claim 4 wherein said first ram position sensing device is also slidably disposed along said path, and wherein means are provided for mechanically coupling said first ram position sensing device to said second ram position sensing device to maintain the overall excursion of said ram between said upper and lower travel limits constant notwithstanding changes in the position of said second ram position sensing device.
 8. A control system as defined in claim 5 which further comprises an actuator arm carried on said ram and arranged to move reciprocatively along said defined operating path therewith, said actuator arm being adapted to actuate said third and second limit switches as said ram descends from said upper travel limit position along said defined operating path.
 9. A control system as defined in claim 4 which further comprises an operator-actuable lead screw for changing the position of said second ram position sensing device.
 10. In a press brake of the type having a frame, a bed, a ram, and drive means on said frame for reciprocating said ram along a defined operating path toward and away from said bed, a control system comprising: means comprising a first limit switch positioned along said operating path for limiting the maximum upward travel of said ram; means comprising a second limit switch slidably mounted on said frame along said operating path for limiting the maximum downward travel of said ram, the position of said second limit switch being operator-adjustable to effect changes in the downward travel limit of said ram to accommodate variations in the thickness of work pieces on said bed; means comprising a third limit switch slidable mounted on said frame along said operating path between said first limit switch and said second limit switch for establishing a work stroke for said ram wherein said ram is advanced toward said bed at a reduced rate beyond a predetermined intermediate location along said path; and means comprising a mechanical coupling between said second limit switch and said third limit switch for automatically repositioning said third limit switch as the position of said second limit switch is changed to maintain the length of said work stroke substantially constant notwithstanding operatorinitiated changes in the downward travel limit of said ram. 